Calculating DRF for 1000V/200A SCRs in 6kV and 1kA string

Step 1: Calculate the number of SCRs in the string
To handle 6kV and 1kA, we need to use a string of SCRs. The voltage rating of the SCR is 1000V, so we need to use at least 6 SCRs in series to handle 6kV. The current rating of the SCR is 200A, so we need to parallel 5 strings of SCRs to handle 1kA.

Step 2: Calculate the total number of SCRs in the circuit
To calculate the DRF, we need to know the total number of SCRs in the circuit. Since we have 6 SCRs in series and 5 strings in parallel, the total number of SCRs in the circuit is 6 x 5 = 30 SCRs.

Step 3: Calculate the holding current of the SCR
The holding current of the SCR is the minimum current required to keep the SCR in the on-state. The holding current for a 1000V/200A SCR is typically around 50mA.

Step 4: Calculate the DRF
The DRF is the ratio of the maximum current to the holding current. We need to calculate the DRF for two scenarios:
i) DRF = 0.1
ii) DRF = 0.2

Step 5: Calculate the maximum current
To calculate the maximum current, we need to divide the total current (1kA) by the total number of SCRs (30). This gives us a maximum current of 33.33A per SCR.

Step 6: Calculate the required holding current
To calculate the required holding current, we need to multiply the maximum current by the DRF.
i) DRF = 0.1, required holding current = 3.33A
ii) DRF = 0.2, required holding current = 6.67A

Step 7: Compare the required holding current with the actual holding current
The actual holding current of the SCR is 50mA, which is much lower than the required holding current. Therefore, the DRF of 0.1 and 0.2 cannot be achieved with a 1000V/200A SCR.

Conclusion
The DRF of 0.1 and 0.2 cannot be achieved with a 1000V/200A SCR. A higher rated SCR or a different configuration of SCRs would be required to achieve the desired DRF.